Multi-channel monopulse direction finding systems can include a monopulse amplitude comparator arranged to communicate four or more channels via a four-quadrant (or more than four segment) aperture. A transmit (Tx) sum channel, a receive (Rx) sum channel, an elevation difference (Delta El) channel, and an azimuth difference (Delta Az) channel are used to determine an angle of arrival in three-dimensions.
Active Electronically Scanned Arrays (AESA), also known as phased array antennas, require accurate phase shift for beam pointing. AESAs require amplitude taper and high phase precision for low side lobe levels (SLL). Precision aperture phase and amplitude control is required for high performance AESAs including a flat, analog like phase with low RMS error, and low SLL analog like amplitude taper with tens of dBs of dynamic range across the array aperture with a tight phase response.
Monopulse antenna systems create three simultaneous beams to process a single radar pulse for precise direction finding. Monopulse antenna system utilize a 4-quadrant aperture dividing a transmit sum beam, a receive sum beam, an elevation difference beam, and an azimuth difference beam. A high central beam gain and low side lobes are desirable in the radiation pattern for the transmit sum beam and the receive sum beam, and a low null signal and low side lobes are desirable in the elevation difference beam and the azimuth difference beam.
Taylor weighting is applied to radiating elements of a monopulse antenna system in order to minimize beam width broadening and to reduce side lobe level gain. For example, FIG. 1 shows a Taylor weighting distribution 20 for a thirty-two element one dimensional array. This Taylor weighting distribution 20 results in two equal side lobe patterns and maximum side lobe gain is about twenty-five decibels below the peak gain of the central beam. The dynamic range of the Taylor weighting distribution 20 is about 8.7 decibels and the pattern provides a flat phase front for the beam.
Bayliss weighting is applied to radiating elements to optimize a null slope for difference beams and to reduce side lobe level gain. A Bayliss weighting provides a negative weight for half of the array. For example, FIG. 1 also shows a Bayliss weighting distribution 24 for a thirty-two element one dimensional array. The maximum side lobe gain is about twenty decibels below the peak gain. The dynamic range of the Bayliss weighting distribution 24 is about 17.8 decibels.
Current monopulse antenna systems cannot utilize both Taylor weighting and Bayliss weighting. Rather, current monopulse antenna systems utilize a split Taylor weighting for difference beams. In a split Traylor weighting, half of the radiating elements in the array follow a normal Taylor weighting distribution and the other half of the radiating elements follow a Taylor weighting with a one-hundred-eighty degree (180°) phase shift resulting in negative weights following the Taylor weighting.
FIG. 2 shows a Taylor weighted gain pattern 28 and a uniform gain pattern 32. The Taylor weighted gain pattern provides an improved beam including lower gain side lobes. FIG. 3 shows a Bayliss weighted gain pattern 36, a split Taylor weighted gain pattern 40, and a uniform gain pattern 44. The Bayliss weighted gain pattern 36 provides significantly lower side lobe gain levels.